I use friendship speed juice swab between shots and in elephant , diamond back , Goex and most recently purchased 25# of Schuetzen , I have only burned a pound or so but not an issue
what did you oil the barrel with after cleaning.
friendship speed juice= 1/3 rubbing alcohal , 1/3 hydrogen peroxide ,1/3 Murphy's oil soap mix and keep in a small spray bottle spray a patch
good thing to snap 3 caps , wipe with a few damp patches then load
for consistency the patch after the shot should be the same going down and coming up each time , I do often flip that patch and put a ball in it just to conserve patches.
the other thing I prefer is 3FG and did find it to burn better especially in the light 25-60gr loads.
whenever I have had hard fouling it usually involved a mineral oil user to protect the barrel for storage after cleaning.